Bio tank/gas replenishment system

ABSTRACT

In systems for treating wastewater liquid by utilizing aerobic biological species, the contaminated wastewater stream is pretreated in a dissolved air flotation system to remove suspended solid waste, including large particles such as fats, grease, and physically emulsified oils. The purified wastewater containing dissolved waste is thereafter gasified and further decontaminated in a bioreactor tank. Biological species in the bioreactor tank consume gas and perform bodily functions that converts dissolved waste into easily removable carbon dioxide and suspend solids. Gas consumed by the biological species is replenished by pumping the wastewater though a liquid-gas mixer. A controller regulates the speed of the pump based on real-time gas concentration measurements provided by a corresponding gas probe disposed within the wastewater in the bioreactor tank.

BACKGROUND OF THE INVENTION

The present invention generally relates to the treatment of contaminatedliquid, such as wastewater. More particularly, the present inventionrelates to a method for removing contaminants from a liquid by use of agas replenishment system that controls levels of dissolved gas in theliquid. The gas contains species capable of converting dissolved solidsinto carbon dioxide and suspended solids, which are more easilyseparated from the liquid than dissolved solids. The present inventionalso pre-treats the wastewater, if needed, to remove large particles,fats, grease, and physically emulsified oils. Membrane separation suchas nano filtration or reverse osmosis is also used to removenon-biodegradable organic materials and inorganic ions.

Industrial wastewater contains various pollutants. Such pollutants arepresent as large particles (larger than one micron), charge stabilizedcolloidal particles (oil and water emulsions, etc.) and dissolvedspecies such as sugar, proteins, or inorganic ions. Regulations requireremoval of most or all of such pollutants before wastewater dischargeinto a publicly owned treatment works (POTW).

Complex treatment methods have been designed to remove the wide varietyof physical and chemical species. In one instance, membrane andseparation processes are used. Micro-filtration is used to remove largeparticles, while ultra-filtration is used to remove colloids andproteins, and reverse osmosis is used to remove ions and small species.But, subsequent cleaning is expensive and often is inefficient as themembranes get fouled with various species present in water. Anotherprocess for removing large particles from water is coagulation withinorganic species, such as ferric ions, ferrous ions, or aluminum ions,to neutralize particle charge. Subsequent sedimentation can be achievedin clarifiers. But, this process is slow and consequently requires largetanks.

Colloidal materials and micro-molecules must be removed after theremoval of larger particles. Biodegradation is a particularly popularway of removing such materials. A collection of active microorganismsthat grow in anaerobic or aerobic tanks may be capable of metabolizingthese biodegradable materials. Anaerobic degradation is generallyefficient, but, it can take months or even years to destroybiodegradable organic pollutants. Aerobic degradation is actually fasterand can be used to treat wastewater with much lower organic loads. Loworganic loads have chemical gas demand (COD) and biological gas demand(BOD) not larger than around 2,000 parts per million (ppm).

Biological aerobic industrial wastewater treatment should use waterhaving high or varying loads of organic materials. Low organic loads canupset the biological aerobic wastewater treatment process.Unfortunately, most industrial wastewater is rich in nutrients andcontinuity varies in composition.

Accordingly, there is a continuing need to provide an industrialwastewater treatment system incorporating aerobic biodegradation whileaccommodating the amount of nutrients in the industrial wastewater overtime. The present invention fulfills these needs and provides furtherrelated advantages.

SUMMARY OF THE INVENTION

The present invention discloses a bio-tank replenishment system fortreating contaminated liquid, such as wastewater. The wastewatercontains biological species capable of converting dissolved solids intocarbon dioxide and suspended solids. The carbon dioxide and suspendedsolids are more easily separated from water than dissolved solids.Wastewater pre-treatment removes large particles, fats, grease, andother physically emulsified oils. Membrane separation, such asnanofiltration or reverse osmosis is also used to removenon-biodegradable organic materials and inorganic ions.

The purified wastewater is transferred to a bioreactor tank for furtherdecontamination therein. Biological species within the bioreactor tankconsume gasses, such as oxygen, nitrogen, carbon dioxide, etc.,dissolved in the wastewater to perform normal aerobic bodily functions.Carbon dioxide and suspended solids are natural by-products of suchbodily functions. The gas concentration in the wastewater must bereplenished so the biological species may continue converting andremoving the dissolved solids within the wastewater.

A gas probe disposed in the bioreactor tank wastewater measuresreal-time gas concentrations therein. A controller responsive to thereal-time gas concentration measurements regulates the gas replenishmentrate of the wastewater via a circulation pump. The circulation pumptransfers wastewater from the tank to a mixer. The controller changesthe speed of the circulation pump according to gas concentrations in thebioreactor tank. The controller also manages the rate of selected gases,such as oxygen, nitrogen, carbon dioxide, etc., entering the mixer, thesize of an evacuated area formed in a wastewater vortex, the size of amixer head space, and pressure within the mixer. The controller controlsthe devices that adjust each of these variables in order to optimize theamount of dissolvable gas within the wastewater during gas replenishmentin the mixer.

The mixer includes a wastewater inlet for receiving the wastewaterstream and a gas inlet for adding selected gases to the wastewater. Thewastewater inlet may comprise hydro-cyclone head inlet that is generallycircular, multi-circular, or has an aspect ratio of 24:1, 10:1, 6:1,2.6:1 or 1:1. Maximum dissolvable gas concentration in the wastewater isdistinct for each hydro-cyclone head inlet and corresponding mixerpressure.

The mixer also includes an accelerator head and a down tube forvigorously mixing the wastewater and gas. The accelerator head spins thewastewater into a vortex in the down tube. Gas inputted into the downtube may form a central evacuated area within the vortex. A sensorintegral to the mixer measures the characteristics of the evacuatedarea, such as size, shape, length, and diameter. The mixer also includesa gasification head space comprising essentially, for example, pureoxygen. Another sensor is capable of measuring the size of the headspace to ensure further efficient gasification of the wastewater streamexiting the down tube. Accordingly, a baffle diverts the gasifiedwastewater from the down tube outlet to the head space. Large gasbubbles not dissolved within the wastewater stream float into the headspace. Additional gas from the head space is dissolved in the wastewaterbefore the wastewater enters the bioreactor tank. A conduit formed inthe top of the mixer retains the non-dissolved gas for selectivereintroduction with the wastewater in the down tube of the mixer.

The gas replenishment system may also be fluidly coupled to a holdingtank, a dissolved air flotation system and a corresponding liquid-solidmixer. The dissolved air flotation system and liquid-solid mixer areused to remove larger particles such as fats, grease, and otherphysically emulsified oils.

Other features and advantages of the present invention will becomeapparent from the following, more detailed description, when taken inconjunction with the accompanying drawings, which illustrate, by way ofexample, the principles of the invention.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings illustrate the invention. In such drawings:

FIG. 1 is a diagrammatic view of a wastewater treatment system embodyingthe present invention;

FIG. 2 is a schematic view of a liquid-solid mixer for use with thepresent invention;

FIG. 3 is a cross-sectional view of the liquid-solid mixer in FIG. 2,taken generally along the line 3-3;

FIG. 4 is a partially sectioned view of a liquid-solid mixer used inaccordance with the present invention;

FIG. 5 is a diagrammatic view of a gravity suspension system forremoving colloidal materials from the wastewater;

FIG. 6 is a schematic view of a bioreactor tank and system for mixinggas and biological species to perform aerobic degradations;

FIG. 7 is an alternative schematic view of a liquid-gas mixer;

FIG. 8 is a sectional view of another liquid-gas mixer usable inaccordance with the present invention;

FIG. 9 is a schematic view illustrating the path of a single particle atthree time intervals within a liquid-gas mixer;

FIG. 10 illustrates schematic representations of the resulting velocityvector of the single particle at the three time intervals shown in FIG.9;

FIGS. 11 a-11 h are diagrammatic representations of various exit valvesincorporated into the liquid-gas mixer; and

FIG. 12 is a chart illustrating the vessel pressure against dissolvedgas content of water for the various exit valves in FIGS. 11 a-11 h.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in the accompanying drawings, for purposes of illustration, thepresent invention resides in a system for treating wastewater liquid toadvantageously utilize aerobic biological species to convert dissolvedsolids into carbon dioxide and suspended solids. As shown in theexemplary drawings for purposes of illustration, the present disclosurefor a wastewater treatment system is referred to generally by thereference numeral 10. Turning now to the representative figures in thespecification, FIG. 1 illustrates the wastewater treatment system 10having a liquid-solid mixer 12 in fluid communication with a floatationtank 14. The floatation tank 14 is a gravity separation system, such asthat described in U.S. Pat. No. 6,797,181, the contents of which areherein incorporated by reference. Once the contaminated wastewater,including large particles, fats, grease, and physically emulsified oilsand the like are removed from the contaminated wastewater via thefloatation tank 14, the purified wastewater is moved to a holding tank16. A pump 18 pressurizes the purified wastewater for transfer from theholding tank 16 into a liquid-gas mixer 20. The liquid-gas mixer 20pressurizes and gasifies the purified wastewater for introduction into abioreactor tank 22. The purified wastewater still contains dissolvedparticles such as sugars, proteins, or inorganic ions that must beremoved before the liquid stream is discharged into a POTW. Theliquid-gas mixer 20 is commonly referenced as a Liquid Cyclone ParticlePositioner (LCPP). The remaining dissolved solids are converted intocarbon dioxide and suspended solids in the bioreactor tank 22. Theremaining waste is thereafter more easily separated from the water inthe bioreactor tank 22 after gasification via the liquid-gas mixer 20.The waste is discharged and the decontaminated water is transferred to aPOTW or the like.

The liquid-solid mixer 12 is fluidly connected to a source of wastewateror other fluid to be treated. Typically, a pump (not shown) is used topressurize and direct a stream of the contaminated wastewater through acontaminated wastewater inlet 24 (FIG. 2) of the liquid-solid mixer 12.As illustrated in FIG. 3, the contaminated wastewater is directedthrough the inlet 24 and into a liquid accelerator 26 that increases thelinear velocity of the contaminated wastewater in the liquid-solid mixer12. The pressurized contaminated wastewater is tangentially acceleratedby the liquid accelerator 26 into a central cartridge 28 of theliquid-solid mixer 12. Here, the pressurized contaminated wastewatercontacts an inner surface 30 (FIG. 4) of the central cartridge 28 athigh velocity and is thereafter forced into a spinning motion within thecentral cartridge 28. Typically, the central cartridge 28 is taperedsuch that a resulting vortex 32 has a larger upper diameter 34 and asmaller lower diameter 36. The contaminated wastewater then exits theliquid-solid mixer 12 through the bottom of a down tube 38 via an exit40. The liquid-solid mixer 12 forces the liquid into a rotational flowsubject to angular momentum. This forms the vortex 32 illustrated inFIG. 2. An additive inlet 42 may introduce gas, chemicals, or solidadditives for treatment of the contaminated wastewater stream.

In a particularly preferred embodiment in FIG. 4, a detailedliquid-solid mixer 12 is shown. The liquid-solid mixer 12 is similar toa hydrocyclone, but, unlike a conventional single port hydrocyclone, theliquid-solid mixer 12 has a 2-stage delivery mechanism. The liquid-solidmixer 12 comprises an upper reactor head 44 and the lower down tube 38through which the contaminated wastewater and mixed additives exit atthe outlet 40 thereof. The liquid-solid mixer 12 is designed such thatthe reactor head 44 imparts a spinning motion to the contaminatedwastewater upon entry via the contaminated wastewater inlet 24. Thevortex 32 forms in the down tube 38 and mixes the additives, liquid,contaminants, and entrained gas typically substantially homogenously.

The reactor head 44 comprises the inlet 24 formed in an outer housing 46such that the contaminated wastewater inlet 24 is in fluid communicationwith a plenum 48. The contaminated wastewater stream flows into thereactor head 44 via the contaminated wastewater inlet 24 and into theplenum 48, as defined by the space between the central cartridge 28 andthe outer housing 46. A base 50 and a lid 52 enclose the remainder ofthe reactor head 44 and seal the plenum 48 to enable pressure build-upwithin the reactor head 44 and corresponding down tube 38. Thecontaminated wastewater stream is pressurized in the plenum 48 aroundthe exterior of the central cartridge 28 disposed within the enclosureof the reactor head 44. The central cartridge 28 is a cylindrical ormulti-faceted member in fluid communication with the down tube 38. Thecentral cartridge 28 includes a plurality of tangential ports 54extending through a cartridge wall 56. The contaminated wastewater isdirected through the tangential ports 54 and into the central cartridge28 at a generally tangential direction to the inner surface 30 thereof.The pressurized contaminated liquid that fills the plenum 48 forcinglyenters the interior of the central cartridge 28 having a spinning motionimparted thereon to form the vortex 32 within the central cartridge 28and the down tube 38. The central cartridge 28 can be configured as ahexagon, octagon, or any other multi-faceted structure. The tangentialports 54 are formed in at least one facet thereof, and more preferablyin every facet thereof as illustrated in FIG. 4. The number of opentangential ports 54, the diameter of the tangential ports 54, thediameter of the inner surface 30 of the central cartridge 28, and thediameter of the down tube 38 determines the speed the contaminatedwastewater spins and passes through the liquid-solid mixer 12.

The tangential ports 54 are configured to receive a plurality ofremovable restrictor plugs 58. Typically, the tangential ports 54 aredrilled and tapped to include threads that allow the removal of thethreaded restrictor plugs 58 via a screwdriver or other tool. Of course,other methods of removably inserting the restrictor plugs 58 within thetangential ports 54 will be appreciated by those skilled in the art. Theamount of mixing energy imparted to the spinning contaminated wastewaterwithin the central cartridge 28 is regulated by the quantity of opentangential ports 54. Inserting the removable restrictor plugs 58 intothe tangential ports 54 decreases the quantity of contaminatedwastewater entering the central cartridge 28 and correspondinglydecreases the rotational speed of the contaminated wastewater therein.Oppositely, removing the removable restrictor plugs 58 from thetangential ports 54 effectively increases the quantity of opentangential ports 54. This increases the flow rate of the contaminatedwastewater into the central cartridge 28 and increases the spinningspeed (mixing energy) of the contaminated wastewater therein. Regulatingthe quantity of open tangential ports 54 also affects the flow rate ofthe contaminated liquid into the central cartridge 28, the volume of thecontaminated wastewater within the central cartridge 28 at any giventime, the pressure in the plenum 48, the central cartridge 28 and thedown tube 38, and the overall process of mixing any additives into thecontaminated wastewater. Such variables help facilitate the process ofhomogeneously mixing said additives within the liquid-solid mixer 12.

Additives, such as pH/redox chemistries, flocculants, coagulants, clay,diotomatious earth, etc. are typically added to the contaminatedwastewater stream to alter the iso-electric chemistry of the mixturethereof and to bind suspended solids therein. The process of adding theadditive is accomplishable upstream of the contaminated wastewater inlet24 formed in the reactor head 44 of the liquid-solid mixer 12. But, theliquid-solid mixer 12 can also include an additive inlet 42 to introducesuch additives immediately before or during mixing. Alternatively, theadditives are added to the contaminated wastewater stream before mixingvia an upstream inlet 60 as shown in FIG. 4. The additive inlet 42, asshown in FIGS. 2 and 4, is formed in the lid 52 of the reactor head 44.Introduction of the additives through the additive inlet 42 creates acentrally evacuated area 62 within the reactor head 44 and extendingdown into the down tube 38. The contaminated wastewater enters thecentral cartridge 28 via the tangential ports 54 having the spinningmotion around the inner surface 30 of the central cartridge 28. Thepressurized introduction of the additives via the additive inlet 42creates the centrally evacuated area 62 by forcing the contaminatedliquid toward the inner surface 30. The spinning contaminated wastewaterstream absorbs and entrains the additives introduced into the mixer 12via the additive inlet 42. The centrally evacuated area 62 formsinterior to the vortex 32 and causes further mixing of the additives andwastewater within a cyclone spin chamber 64. The spinning contaminatedwastewater absorbs and entrains the additives introduced into the mixer12 via the additive inlet 42. A sensor 66 having an upper gauge 68 and alower gauge 70 (FIG. 5) may electrically, sonically, visually, orotherwise measure the size and location of the centrally evacuated area62 within the down tube 38. Furthermore, the sensor 66 may be used todetermine the size, characteristics, and termination location of thecentrally evacuated area 62 and the physical shape of the vortex 32. Acontroller determines the amount of replenishment additives needed toreplace the additives absorbed into the contaminated wastewater streamand carried out through the outlet 40 and into the floatation tank 14.

It was conventionally thought that longer mixing time (1-10 minutes) atlower mixing energies (30-100 revolutions per minute [RPM] of a mechanicmixer) was needed for optimum flocculation. But, this is not the case.Shorter mixing times (5-10 seconds) with higher mixing energies (up to4,000 RPM with a mechanical mixer) yielded cleaner water with lowerturbidity and larger, easier floating flocs. Thus, the mixing inside thecentral cartridge 28 of the liquid-solid mixer 12 may last only a fewseconds while yielding excellent flocs without any mechanical pre-mixingor potential polymer breakage. Mixing energy or speed at which thecontaminated wastewater is passed through the liquid-solid mixer 12 isdetermined in large part by the number of open tangential ports 54 setto receive the contaminated wastewater, as previously discussed.

A plurality of the liquid-solid mixers 12 may be used together dependingupon the type and quantity of chemical additives, desired mixing energy,and desired mixing time required to optimize separation. The integrationof such a plurality of the liquid-solid mixers 12 is more fullydescribed in U.S. Pat. No. 6,964,740, the contents of which are hereinincorporated by reference. Such a plurality of the liquid-solid mixers12 allows sequential injection of additives at optimum mixing energiesand for optimum mixing durations for each chemical constituentindividually. Additionally, the amount and type of additives, the sizeand location of the centrally evacuated area 62, the speed, pressure andflow rate of the contaminated wastewater in the vortex 32, and the sizeof the down tube 38 may all be varied within each respectiveliquid-solid mixer 12.

FIG. 5 illustrates the process of removing solid waste from thecontaminated wastewater stream via dissolved air floatation (DAF). Thecontaminated wastewater having the chemical additives added thereinexits the liquid-solid mixer 12 at the outlet 40 and flows through atube 72, a pressure valve 74 and into a nucleation chamber 76. Thepressure valve 74 regulates the flow rate of the contaminated wastewaterstream having the mixed chemical additives therein. The flow rate of thecontaminated wastewater into the nucleation chamber 76 and through acavitation plate 78 directly affects the rate of nucleation andflocculation of the solid waste particles within the contaminatedwastewater. In general, the floatation tank 14 removes the solid waste80 from the contaminated wastewater and filters the purified wastewaterfrom the floatation tank 14 via a purified wastewater outlet 82. Removedpurified wastewater is stored in the holding tank 16 (FIG. 1).

More specifically, the generally homogenous contaminated wastewaterstream flows into the nucleation chamber 76 via the tubing 72. Thecavitation plate 78 disposed within the nucleation chamber 76 has aplurality of apertures (not shown) formed therein to initiate nucleationand bubbling before the wastewater stream enters a corresponding bloomchamber 84. The bubbles that form in the nucleation chamber 76 areextremely small and attached to the flocculants within the contaminatedwastewater stream. The resulting bubbles combine and increase in size inthe bloom chamber 84. A solid flocculant froth of the solid waste 80forms at the surface of the floatation tank 14 as the small bubblesincrease in size and float to the top thereof. The solid waste 80 isskimmed from the surface of the floatation tank 14 via a set of paddles86. The skimmed solid waste 80 is placed in a dewatering subsystem 88.The denser treated wastewater (purified wastewater 90) sinks to thebottom of the floatation tank 14 for removal thereof via the purifiedwastewater outlet 82. The purified wastewater is thereafter stored inthe holding tank 16 (FIG. 1) before being pumped into the liquid-gasmixer 20 for eventual treatment in the bioreactor tank 22. The purifiedwastewater in the holding tank 16 still contains additives and othernano-particle waste therein. Such additives and waste are accordinglyremoved via the bioreactor tank 22. Further water extracts from thedewatering subsystem 88 are re-circulated back into the liquid-solidmixer 12 for reprocessing. The corresponding solid waste 80 in thedewatering system 88 is thereafter removed from the treatment system 10altogether.

FIG. 6 is a diagrammatic illustration showing the purified wastewaterbeing further treated by the bioreactor tank 22. The purifiedwastewater, as shown in FIG. 1, is transferred from the holding tank 16to the bioreactor tank 22 via the pump 18 and the liquid-gas mixer 20.The purified wastewater pumped from the holding tank 16 (FIG. 1) isdenoted as a liquid source 90 in FIG. 6. The liquid source 90encompasses any liquid stream capable of being treated within the scopeof the bioreactor tank 22. Preferably, the liquid source 90 is thepurified wastewater stored in the holding tank 16. The purifiedwastewater is introduced into the liquid-gas mixer 20 via a purifiedwastewater inlet 92. In the embodiment of FIG. 6, the liquid-gas mixer20 includes a second re-circulation inlet 94 that receives partiallytreated purified wastewater from a tank 96 via a circulation pump 98 anda corresponding re-circulation line 100. A controller 102 connected toan gas probe 104 regulates the re-circulation pump 98 to optimize thecirculation of the purified wastewater within the bioreactor tank 22, asis more fully described herein. The controller 102 is also connected tothe other components of the treatment system 10, including the variouspumps, valves, cavitation plates, mixers (liquid-solid and liquid-gas),inlets, outlets, fans, sensors and the dewatering subsystem 88components. The controller 102 processes information gathered from thesedevices and, accordingly, manages the overall treatment system 10 viathese devices.

The liquid-gas mixer 20 integrated into the bioreactor tank 22 isdistinguishable from other liquid-gas mixing devices. For instance, inM. L. Jackson, “Energy Effects in Bubble Nucleation,” Industrial andEngineering Chemistry Research, Vol. 33, pp. 929-933 (1994), it wasshown that much higher gas transfer in bubble nucleation efficienciesare achieved if gas is saturated into liquid at lower pressure and thenpumped or transferred into a floatation tank at higher pressure. Theliquid-gas mixer 20 is an ideal device to achieve such liquid-gasmixing. Pressure inside of the liquid-gas mixer 20 can always bedifferent from the pressure used to pump the purified wastewater stream.Pressure is usable to precisely adjust gas dosage (oxygen, ozone, carbondioxide, nitrogen) to replenish the saturation pressure gas loss withinless than 1%. Increasing the flow rate of the purified wastewaterenables delivery of 37 ppm of gas at 15 pounds per square inch (psi) asefficiently as at 90 psi. Higher gas concentrations are slower toachieve at lower pressure, while increasing flow rate (transferpressure) achieves almost equal gas rates faster. Using one or twoliquid-gas mixers 20 at low pressures is therefore more efficient thanusing one liquid-gas mixer 20 at a very high pressure.

Important to the process of the bioreactor tank 22 is the fast andefficient biodegradation of saturated sludge particulates via aerobicmicroorganisms embedded within food particles, dissolved organics, andoxygen. The liquid-gas mixer 20 is, for similar reasons as theliquid-solid mixer 12, an excellent mixer with high collisionefficiencies. Microorganisms are large enough to be moved likeparticulates throughout the liquid-gas mixer 20, similar to the spinningmotion imparted to the contaminated wastewater and additives in thecentral cartridge 28 of liquid-solid mixer 12. Thus, the microorganismshave varying angular and vertical velocities within a cyclonic mixer 106(FIGS. 7 & 8). As in the case of gas (gas), such movement at highvelocity significantly enhances destruction of gradients in gas and infood concentration near the microorganisms because the microorganismsconsume food and gas (oxygen) nearby and create such gradients. Suchmixing also aims to remove gradients in concentration of the products ofmicrobial metabolism.

The angular movement of a microorganism 108, represented by the dot inFIG. 9, is illustrated in three sequential positions within the cyclonicmixer 106 of the liquid-gas mixer 20. The position of the microorganism108 is shown in three separate time periods denoted by T₁, T₂, and T₃.The time sequences T₁, T₂, and T₃ illustrate the position of themicroorganism 108 at various radial positions within the spiralingpurified wastewater stream within the cyclonic mixer 106. Thecorresponding times T₁, T₂, and T₃ correlate to the three various radiir₁, r₂, and r₃, respectively, of the spiraling purified wastewaterstream within the cyclonic mixer 106. FIG. 10 charts resulting velocityvectors 110, 110′, 110″ of the microorganism 108 at the three exemplarytime periods T₁, T₂, and T₃. The resulting velocity vector 110 is mainlyradial when the microorganism 108 is adjacent to the solid inner-surfaceof the cyclonic mixer 106. The resulting velocity vectors 110′, 110″become predominantly axial, or extending downwardly into the cyclonicmixer 106, as the microorganism 108 moves toward the center of thecyclonic mixer 106 at times T₂ and T₃. The microorganism 108 is definedin the illustrations in three distinct locations at three sequentialtimes. But, it is to be understood that time is a continuum and thusradial and actual velocity of the microorganism 108 is in continuousflux.

The present disclosure illustrates two types of liquid-gas mixers 20,20′ in FIGS. 7 and 8, respectively. These liquid-gas mixers 20, 20′entrain gas and liquid such that the aerobic activity of the biologicalmicroorganisms may further clean the purified wastewater processed inthe bioreactor tank 22. Specifically, the liquid-gas mixers 20, 20′ areused to dissolve and entrain gas in the purified wastewater stream. Theliquid-gas mixers 20, 20′ are similar in construction and operation.Similar reference numerals are identified on each of the liquid-gasmixers 20, 20′ to denote similar or identical components.

Purified wastewater from the holding tank 16 or the floatation tank 14is pumped through the purified wastewater inlet 92, 92′ and into thecyclonic mixer 106, 106′. The cyclonic mixer 106, 106′ includes anaccelerator head 112, 112′ for imparting a spinning motion to thepurified wastewater stream. The accelerator head 112, 112′ is similar tothe tangential ports 54 formed in the central cartridge 28 of thereactor head 44 in FIG. 4. In one embodiment in FIG. 7, the cyclonicmixer 106 is a generally straight tube extending the length of apressure chamber 114. Alternatively, as illustrated in FIG. 8, thecyclonic mixer 106′ is varyingly shaped, including being tapered. Inboth instances, the cyclonic mixers 106, 106′ extend to approximatelythe bottom of the vessel 114, 114′.

Compressed gas or air is introduced into the purified wastewater streameither upstream of the accelerator head 112, 112′ or downstream viaplacement directly into the cyclonic mixer 106, 106′. As illustrated inFIGS. 7 and 8, a gas inlet 116, 116′, respectively, is in fluidcommunication with the purified wastewater inlet 92, 92′. Alternatively,gas, such as oxygen or air, may also be introduced directly into thevessel 114, 114′ via an inlet/outlet 118, 118′. The inlet/outlet 118,118′ helps maintain a head space 120, 120′ of compressed gas to furthergasify the purified wastewater within the vessel 114, 114′. If less gasin the vessel 114, 114′ is desired, the head space 120, 120′ isdecreased by opening the inlet/outlet 118, 118′ to allow the pressurizedgas within the head space 120, 120′ to escape. The head space 120, 120′may also be decreased by releasing and recycling gas back into the downtube 106, 106′ by means of a conduit 121, 121′. Oppositely, theinlet/outlet 118, 118′ is opened and pressurized gas is added to thehead space 120, 120′ of the vessel 114, 114′ to increase the amount ofgas within the head space 120, 120′ of the vessel 114, 114′. Gas in thehead space 120, 120′ is entrained in the purified wastewater afterexiting the cyclonic mixer 106, 106′. The gasified purified wastewaterexits the cyclonic mixer 106, 106′ and flows upward from the bottom ofthe cyclonic mixer 106, 106′ and through the angular base formed by abaffle 124, 124′. Accordingly, the purified wastewater exits the baffle124, 124′ near the top of the vessel 114, 114′. Large bubbles notentrained in the purified wastewater stream immediately rise to the headspace 120, 120′. The remaining gasified purified wastewater and smallentrained bubbles within the vessel 114, 114′ flow downwardly to adischarge outlet 122, 122′ and into the bioreactor tank 22 for furtherprocessing and decontamination in the tank 96. The aerobicmicroorganisms use the gas to convert the dissolved solids intosuspended solids and carbon dioxide in the tank 96. As further shown inFIG. 7, a gas sensor 126 monitors the size of the head space 120 bysensing the amount of compressed gas within the vessel 114. The gassensor 126 is in electrical communication with the controller 102 suchthat optimal gas content is dissolved within the purified wastewaterstream before placement into the tank 96. Compressed air is added to thevessel 114 while the head space 120 is above the upper gas sensor 128and the compressed gas supply is shut off when the head space 120 fallsbelow the lower gas sensor 130.

The gasified purified wastewater stream exits the liquid-gas mixer 20,20′ into the tank 96 via a discharge orifice 132 as shown in FIG. 6.Microorganisms within the tank 96 are circulated via a fan 134 submergedwithin the purified wastewater. Corresponding gas levels within the tank96 are monitored by the gas probe 104. Controlling dissolved gas levelsis necessary to promote the activity of the biological species. Thebiological species are the instrument through which the dissolvedcontaminates are more easily separated from the purified wastewater. Thebiological species consume dissolved gas from the water to performnormal bodily functions. Tremendous quantities of organic agents arenecessary to convert contaminants in the purified wastewater fromdissolved to suspended solids. Accordingly, tremendous amounts of gasmust be replaced to promote such a conversion.

The rate of gas consumption in the process of the present invention isnot fixed due to the complex variety of biological species in theby-products that each species produces. Gas consumption rates arerelatively slow at the beginning of the process. Biological speciesdivide and increase in population once a particular dissolvedcontaminant in the purified wastewater is consumed. Such a particularspecies may increase in size by a factor of two. These offspring repeatthe process and consume more dissolved contaminants. The gas depletionrate increases as the population of species grows until either thecontaminant level is depleted or the available dissolved gas level isdepleted. In either case a specific species population begins todwindle.

The result of such a “rise” and “fall” of biological activity is ageneration of by-products that must, in turn, be consumed by a secondset of biological agents. The second set of biological agents go througha similar “rise” and “fall” cycle as the original set of biologicalagents. The process, again repeats, for the corresponding third set ofbiological agents and so on. The process continues to repeat and cyclethrough a given amount of biological species within the purifiedwastewater. The process continues until all by-products of theconsumption tail off. Dissolved gas is consumed by each succeeding waveof biological species in this process. The overall consumption of thedissolved gas dwindles with the amount of generated by-product.

The present invention addresses this fluctuation in dissolved gascontent by use of the dissolved gas probe 104 submerged in the purifiedwastewater in the tank 96. The controller 102 receives a signal from thedissolved gas probe 104 in order to properly regulate the gas contentwithin the purified wastewater in the tank 96. The controller 102 mayregulate the re-circulation pump 98 and/or activate or disable any ofthe aforementioned inlets via the gas replenishment system. In oneembodiment, the wastewater treatment system 10 economically maintainsthe desirable dissolved gas levels in the tank 96 via a series of pumpsattached to a plurality of gas replenishment systems, each usingdifferent gases or gas blends as needed. The controller 102 activatesthe gas entrainment systems that infuse the purified wastewater withconcentrated blends of gas to economically regulate the dissolved gasdemand increases from the microorganisms during high gas demand periods.The controller 102 deactivates the various gas systems as gas demandsdwindle. The controller 102 may favor systems that use compressedatmospheric air instead of using a pure gas, such as oxygen.

As shown in FIG. 6, the purified wastewater in the tank 96 may bere-circulated back into the liquid-gas mixer 20 by means of there-circulation pump 98 and corresponding re-circulation line 100. There-circulation pump 98 is a key mechanism in replenishing the gas supplywithin the purified wastewater stream. The re-circulation pump 98ensures that the purified wastewater is able to be replenished with gasvia the liquid-gas mixer 20. The liquid-gas mixer 20, via the cyclonicmixer 106, is responsible for the efficient particulate contact anddissolution of gases (oxygen) in the wastewater stream. The particlemovement within the cyclonic mixer 106, as previously described, isimportant for efficient gasification of the purified wastewater stream.As was shown in FIGS. 9 and 10, the microorganisms move throughout thecyclonic mixer 106 with varying angular velocity and vertical velocity.This “in” to “out” movement mixes the gas bubbles with the waterclusters throughout the cyclonic mixer 106. Centrifugal force thencauses bubble breakup inside “hungry” water molecules having nodissolved gas. Such a process avoids a gradient of gas concentrationbuildup near the gas/water interface. Such gradients oppose further gasdissolution until gas molecules move to the water layers with nodissolved gas. In other words, diffusion is slow. If other mixingdevices with similar high energy (high liquid RPMs) are used, bubblecoalescence occurs with subsequent loss of gas into the atmosphere.Bubble loss limits the maximum amount of gas economically dissolvable inthe wastewater. In the liquid-gas mixer 20, gasification occurs withinthe cyclonic mixer 106 and the corresponding pressurized vessel 114. Gasnot entrained with the purified wastewater stream bubbles up and formspart of the head space 120, for later gasification. Hence, no gasescapes and such gas that does bubble out from within the wastewaterstream is effectively recaptured and reused.

Effective use of the “in” to “out” movement of the gas bubbles at highvelocities significantly enhances destruction of the gradients. Suchmixing also aims to remove gradients in concentration of the products ofmicrobial metabolism. Acceleration within the cyclonic mixer 106 usuallyranges from 25-100 G's during routine operation. Even though theresidence time of the purified wastewater in the cyclonic mixer 106 isonly a fraction of a second, the rapid acceleration of the bubbles (orany particulates) traverse the short distance across the cyclonic mixer106 (typically 1 centimeter [cm] for a 15 cm diameter unit) inmilliseconds. The small bubble size (large surface area), large bubbleflux, and the kinetic paths of the bubbles through the cyclonic mixer106 facilitate high rate gas transfer with small gas loss. This resultsin the excellent ability to remove volatile organic species or to aerate(gasify) water, if desired.

It is well known to those skilled in the art that subsequentlydepressurizing supersaturated pressurized air produces small bubbles.Such bubbles are, for instance, produced in the dissolved air floatationprocess and are as small as 20 microns. Although, technologies that usepressurized gases with mechanical impeller stirring do not result insimilar efficiencies. Bubble breakup, gas dissolution, particle toparticle collisions, particle to bubble to polymer collisions, polymeruncoiling, etc. are particular problems in other systems.

FIG. 12 illustrates levels of entrainment obtained using a set of eighthydro-cyclone reactor heads 136 a-136 h illustrated in FIGS. 11 a-11 h.The hydro-cyclone reactor heads 136 a-136 h have various cyclone inletaspect ratios as illustrated. These aspect ratios include 24:1 (FIG. 11a); 10:1 (FIG. 11 b); 6:1 (FIG. 11 c); 2.6:1 (FIG. 11 d); 1:1 (FIG. 11e); circular (FIG. 11 f); four small circles (FIG. 11 g); and a showerhead arrangement (FIG. 11 h). FIG. 12 illustrates the dissolved oxygencontent of water (in ppm) per vessel pressure (in psi) using the varioushydro-cyclone reactor heads 136 a-136 h of FIGS. 11 a-11 h. Theselection of the hydro-cyclone reactor head can dramatically affect theamount of dissolved oxygen entrained or otherwise introduced into theliquid. The vessel pressure is determined by the pressure of the liquidintroduced into the liquid-gas mixer 20, the size of the inlet 92, andthe diameter of the cyclonic mixer 106. The appropriate hydro-cyclonereactor head plate is selected with a known vessel pressure to obtainthe desired level of dissolved gas content in the purified wastewaterstream discharged from the liquid-gas mixer 20.

The remaining inorganic ions or non-biodegradable organic materialsremaining in the wastewater can be removed by membrane separations.Virtually all of the other contaminants have been removed at this point.Thus, the membranes are less susceptible to failing or clogging.Accordingly, a decontaminated water discharge outlet 138 removes thesubstantially cleaned and decontaminated water from the tank 96.

Although various embodiments have been described in detail for purposesof illustration, various modifications may be made without departingfrom the scope and spirit of the invention. Accordingly, the inventionis not to be limited, except as by the appended claims.

1. A bio-tank gas replenishment system, comprising: a cyclonic two stagemixer for mixing wastewater with a selected gas, wherein the mixerincludes a head including a gasification head space, an outer housinghaving a wastewater inlet in fluid communication with a plenum definedby a space between the outer housing and an inner cartridge, the innercartridge having a plurality of ports which are selectively opened andclosed to permit wastewater flow therethrough and into a down tube; asensor for measuring the size of the head space; a bioreactor tank forprocessing the wastewater mixed with the selected gas; a probe formeasuring gas concentration of the wastewater in the bioreactor tank; acontroller responsive to the probe measurements, wherein the controllerregulates mixer pressure thereby regulating the gas concentration of thewastewater in the bioreactor tank; and a circulation pump fortransferring wastewater from the bioreactor tank to the mixer, whereinthe controller sets the circulation pump speed to optimize thewastewater gas concentration.
 2. The system of claim 1, wherein themixer includes a hydro-cyclone head inlet.
 3. The system of claim 2,wherein the hydro-cyclone head inlet is generally circular,multi-circular, or has an aspect ratio of 24:1, 10:1, 6:1, 2.6:1 or 1:1.4. The system of claim 3, wherein the maximum dissolvable gasconcentration in the wastewater is distinct for each hydro-cyclone headinlet and corresponding mixer pressure.
 5. The system of claim 1,wherein the controller sets the circulation pump speed based on gasconcentration information provided by the probe.
 6. The system of claim1, wherein the head comprises an accelerator head for spinning thewastewater into the down tube.
 7. The system of claim 6, wherein thespinning wastewater forms a vortex in the down tube, the vortexincluding a central evacuated area.
 8. The system of claim 1, includinga port for changing the size of the head space in response to input fromthe sensor.
 9. The system of claim 8, including a baffle for divertinggassated wastewater from a down tube outlet, to the head space.
 10. Thesystem of claim 8, including a conduit for transferring gas from thehead space for remixing with the wastewater.
 11. The system of claim 8,wherein the controller receives real-time gas concentration informationfrom the probe.
 12. The system of claim 1, wherein the mixer includes awastewater inlet and a gas inlet, the wastewater inlet being fluidlycoupled to a holding tank.
 13. The system of claim 12, wherein theholding tank is fluidly coupled to a dissolved air flotation system anda corresponding liquid-solid mixer.
 14. The system of claim 1, whereinthe gasification head space comprises essentially a pure selected gas.15. The system of claim 1, including plugs removably insertable into theports of the cartridge for increasing or decreasing the wastewater flowthrough the mixer.
 16. A bio-tank gas replenishment system, comprising:a cyclonic mixer for mixing wastewater with a selected gas, wherein themixer includes a hydro-cyclone head inlet, a wastewater inlet and a gasinlet, an accelerator head for spinning the wastewater into a vortex ina down tube, the vortex including a central evacuated area, a probe formeasuring gas concentration of the wastewater in the tank, angasification head space, a sensor for measuring the size of the headspace, a port for changing the size of the head space in response toinput from the sensor, and a baffle for diverting oxygenated wastewaterfrom a down tube outlet, to the head space; a bioreactor tank forprocessing the wastewater mixed with the selected gas; a probe formeasuring gas concentration of the wastewater in the bioreactor tank;and a controller for regulating the gas replenishment rate of thewastewater.
 17. The system of claim 16, wherein the wastewater inlet isfluidly coupled to a holding tank, which is fluidly coupled to adissolved air flotation system and a corresponding liquid-solid mixer.18. The system of claim 16, wherein the hydro-cyclone head inlet isgenerally circular, multi-circular, or has an aspect ratio of 24:1,10:1, 6:1, 2.6:1 or 1:1.
 19. The system of claim 18, wherein the maximumdissolvable gas concentration in the wastewater is distinct for eachhydro-cyclone head inlet and corresponding mixer pressure.
 20. Thesystem of claim 16, including a conduit for transferring gas from thehead space for remixing with the wastewater.
 21. The system of claim 16,wherein the gasification head space comprises essentially a pureselected gas.
 22. The system of claim 16, wherein the cyclonic mixercomprises a two-stage mixer.
 23. The system of claim 22, wherein thecyclonic mixer includes an outer housing having a cartridge therein, anddefining a plenum therebetween, the cartridge having a plurality ofports selectively opened and closed to control the flow of wastewaterinto the down tube.
 24. The system of claim 23, including plugsremovably insertable into the ports of the cartridge for increasing ordecreasing the wastewater flow through the mixer.
 25. The system ofclaim 16, including a circulation pump for transferring wastewater fromthe bioreactor tank to the mixer.
 26. The system of claim 25, whereinthe controller sets the circulation pump speed based on real time gasconcentration information provided by the probe.